The present invention is particularly adapted for use in conjunction with torque transfer devices in the nature of multi-plate, brake packs that are hydraulically and/or mechanically actuated. Such multi-pack, brake packs are often employed with the individual transmission output shafts, or the axle assemblies connected thereto. Such brake packs are generally actuated by axial compression to effect the desired braking action in response to the depression of a brake pedal. That is, the compression of the multiple plates with the friction disks therebetween effects the torque transfer which actually slows the vehicle.
The durability, and hence the life span, of such multi-plate, brake packs is dependent upon the application of a coolant, generally a cooling fluid, to the brake packs prior to the actuating compression thereof. Simply stated, the heat that can be generated within brake packs which are not adequately precooled will distress the successively stacked plates and friction disks therein and ultimately lead to an untimely failure of the brake pack.
The preferred brake apply valves do make provision for pre-cooling, but such pre-cooling is induced by the initial depression of the brake pedal. That type arrangement can work quite well under appropriate conditions. However, in those instances where the driver depresses the brake pedal much more rapidly than normal--as in a panic stop--the pre-cooling flow might not be initiated in time for the necessary coolant to have reached the brake packs prior to their compression.
Other conditions which might also delay the desired flow of the coolant until after compression of the brake packs has been initiated are: positioning the brake coolant valve at a location which is sufficiently remote from at least one brake pack that the pre-cooling bath can not begin prior to compression of the brake packs; or, using a coolant delivery system configuration which allows the cooling fluid to drain from a significant portion of the system when the brakes are not being applied, thus requiring that the system replenish the fluid therein before the pre-cooling bath can begin.
Also, in many track laying vehicles, brake systems employ both mechanical and hydraulic apply mechanisms. With these integrated systems, the usual applied sequence is mechanical before hydraulic. The mechanical applied portion will generally use a cam-apply mechanism which will increase mechanical advantage. When the hydraulic applied portion comes into effect, the mechanical input reaction is reduced such that the operator must be alert to the change in reaction force which is felt at the brake pedal. While experienced operators are not overwhelmed by this system, it would be preferable to alleviate this condition.